The subject matter disclosed herein relates generally to rotary wing aircraft, and in particular to optically tracking blades of a rotary wing aircraft.
In the field of rotary wing aircraft, it is desirable to track blade motion. Rotating blades of a helicopter main rotor undergo an extremely complex motion trajectory with severe load conditions in a harsh environment. The on-board measurement of such rigid body motion at the root of the blade constitutes a major challenge for the helicopter industry. This measurement is particularly difficult for blades mounted to an elastomeric hinge-less bearing where the three angular motions (flap, pitch and lead-lag) are highly coupled and the elastomeric bearing pivot center shifts along the blade span due to centrifugal acceleration that varies with aerodynamic load and flight regimes. Existing methods to determine the blade motion in real time and in a non-contact fashion include holographic, Morie and laser Doppler vibrometer techniques. These non-contact optical measurement methods are only able to track one degree of freedom of motion at a time and may often fail to measure both statically and dynamically. They may also be very complex, bulky and unreliable in the main rotor environment and only appropriate for the laboratory environments and wind tunnel tests. Other methods of integrating acceleration from accelerometers or gyroscopes usually require added sensors or prior knowledge of the motion characteristics to remove drift due to integration and may be incapable of measuring static and low frequency motion of the main rotor blade.